Question

a=7,a13=35 find d and s13

Answer 1

Heya mate.....

a=7

a13=35

a13=a+12d-------(1)

Put value of a in (1)

We get...

35=7+12d

12d=28

d=7/3

S13 = n/2 [a+l]

n=13, a= 7, a13 = l = 35

S13 = 13/2 [7+35]

S13 = 13/2 [42]

S13 = 13 [21]

therefore, S13 = 273

Hope it helps u☺

@skb

Answer 2

Answer:

d = 7/3, Sn=273

Step-by-step explanation:

First term of an AP = a = 7

Thirteenth term of an AP = 35

a + 12d = 35 ------(1)

Substitute a in eq - (1)

a + 12d = 35

(7) + 12d = 35

12d = 35 - 7

12d = 28

d = 28/12

d = 7/3

In an AP sum of the terms = n/2 ( a + an )

= 13/2 ( 7 + 35)

= 13/2 ( 42)

= 13(21)

= 273